The present invention relates in general to rotary machines of the type comprising a stator and a rotor, such as motor vehicle alternators.
An alternator rotor is known that comprises two plates carrying mutually interleaved pole pieces or claws. Permanent magnets are disposed in the gaps between adjacent pole pieces, being carried by support strips passing beneath the pole pieces. That rotor suffers from the drawback that the space occupied by the strips reduces the volume available inside the rotor beneath the pole pieces. In addition, it requires the magnets to be put into place prior to assembling the plates together, and that can be difficult or awkward depending on how the assembly line is organized.
An object of the invention is to provide an alternator of a different type that makes it possible to increase the inside volume of the rotor.
To achieve this object, the invention provides a vehicle alternator comprising a rotor having interleaved pole pieces, permanent magnets disposed between the pole pieces, and at least one magnet-support strip, in which the or each strip extends over a circumferential outside face of the pole pieces.
Thus, the segments of the or each strip contiguous with the pole pieces (which are generally longer than the segments contiguous with the magnets) do not eat into the inside volume of the rotor. In addition, this disposition makes it possible in most cases for the or each strip and the magnets to be put into place after the pole pieces have been interleaved by assembling the plates together.
Advantageously, the or each strip extends over a circumferential outside face of the magnets.
This further increases the volume available inside the rotor. In addition, it is always possible to put the magnets into place after the pole pieces have been interleaved, e.g. by winding the strip(s) around the axis of the rotor.
Advantageously, the or each strip occupies a complete turn about the axis of the rotor.
Advantageously, the pole pieces present respective grooves for receiving the or each strip.
This prevents increasing the size of the rotor in the air gap.
Advantageously, the groove has a radial dimension relative to the axis of the rotor which is greater than the corresponding dimension of the associated strip.
In this way, the strip does not eat into the outside diameter of the rotor.
Advantageously, the groove is contiguous with a chamfer or with an axial end face of the pole pieces relative to the axis of the rotor.
Advantageously, the or each strip presents support segments contiguous with the magnets and intermediate segments extending between the magnets and of a width parallel to the axis of the rotor that is less than the corresponding width of the support segments.
This saves material in the intermediate segments without harming the quality of the support of the magnets on the support segments.
Advantageously, the magnets are stuck to the strip(s).
The invention also provides a method of manufacturing an alternator, which method includes a stage of assembling a rotor, which stage comprises the steps consisting in:
interleaving pole pieces; and
fitting at least one strip carrying permanent magnets on a circumferential outside face of the pole pieces so as to place the magnets between the pole pieces.
Advantageously, the or each strip is put into place by being rolled onto the pole pieces about the axis of the rotor.